Regulars here are aware of what we call post-midnight series on the channel (broadcasts kept quiet but believed needed for licencing), and there's a movie factor to this as well which hasn't been mentioned yet.
I've found that the best way to look out for a wanted movie is to do the hard work - check the full listings of 104 MM Premiere on a regular basis. (Another website I've used for years which tries to look out for items for people unfortunately fails too often.)
As a result I've discovered a number of good movies that are not publicised and are broadcast at odd times, usually post-midnight but not always.
Some do repeat, though not usually in my knowledge.
What is their purpose?
I believe also just broadcast to meet licencing requirements as there's then no plan for the mass broadcast environment, I think some were even on Box Office so we believe this just makes it legal or cheap in some circumstances.
Is it a secret?
Well it's not something they can get upset about us discovering or discussing as we're doing nothing wrong, but they're clearly trying to hide these activities... ;-)
Next example is this afternoon - @ 1325 - "Breaking The Bank"
(This one's older (2014) so may have been on before, but no repeats seen.)